Recently, an image processing apparatus, for example, a copying machine which is capable of enlarging and reducing has been spread through the world. Such a copying machine, which can easily provide copying images of a desired magnification for document images, is in common use for copying maps, design drawings of machines and buildings and the like.
Further, as to such kind of a copying machine, a digital copying machine is also in common use. The digital copying machine reads scanned document images by using an image pickup element such as a CCD (Charge Coupled Device) sensor, etc. and stores the image data in an image memory. The digital copying machine then enlarges or reduces the image data, and outputs the image data. Since such a machine temporarily stores image data of a document the an image memory, it is easy to enlarge or reduce the image data.
In the processes of enlargement and reduction, longitudinal and lateral magnifications may be set differently. Further, a copying magnification is suitably set by an operator (manual magnification setting), or automatically set according to a size of a copy sheet (automatic magnification setting).
However, with respect to processes of enlargement and reduction, since a conventional digital copying machine is capable of only enlarging or reducing a whole image, the function is low in spite of the advantage of an easy process for image data, thereby causing low added value.
Therefore, an image processing apparatus such as the above-mentioned copying machine is hoped to be developed so as to have a function which can solve following problems and so as to rise added value of the apparatus.
For example, although design drawings of machines and buildings are made in an exact dimension or an accurate magnification, when they are copied by a copying machine, the copy image is very difficult to determine whether a dimension of the copy image is same as the exact dimension, enlarged, or reduced. Furthermore, after enlarging and reducing are repeated, the magnifications of the drawing becomes difficult to be discriminated. As a result it is hard to grasp the exact dimension.
In addition, since blank portions were also enlarged or reduced, when a drawing is returned to its exact dimension, there cause problems that the image is too large or too small for a specified size of sheets. More specifically, it is very troublesome to return a drawing to its original aspect ratio after the lengthwise and breadthwise magnifications of the drawing have been set separately so as to be copied. Further, during a copying operation, a distortion of a copy image may occur, due to lifting or twisting of a document, so that the copy image inclines.
Incidentally, when you want to know the distance of a specified section of a road shown in a map, you have took the measure of the distance on the map by using a ruler, and multiplied the measured value by a reduction value of the map. However, such a way requires a lot of troublesome works such as measuring a length and multiplying the measured length by a reduction value of the map. In addition, since the length is measured on the map, the accurate distance cannot be obtained. When an exact dimension and a scales of a reduction value are not shown in a map, it is almost impossible to know a dimension and a distance.
In not only a copying machine but also a facsimile and an image processing apparatus having a scanner, it is occasionally difficult to process read image data because of inaccuracy of a dimension and a distance, an error in the magnification of a lengthwise magnification to a breadthwise magnification, distortion of a copy image, etc.